The present invention can be used in a particularly advantageous but nonlimiting manner in wireless communication systems of the M2M (Machine-to-Machine) type or of the “Internet of Things” (IoT) type.
In the context, for example, of the IoT, each object of everyday life is destined to become a communicating object, and, to this end, is equipped with a terminal suitable for transmitting data to an access network. However, it is understood that, insofar as is possible, the cost of the terminal should not significantly impact upon that of the object to which it is added, such as to make many objects of everyday life communicate. As a result, the complexity of the terminals must be reduced as far as possible, in order to reduce the manufacturing cost thereof.
To this end, in a wireless communication system for the IoT, the terminals are preferentially not synchronized with regard to time and frequencies with the access network, and alone decide the transmission instants and the transmission frequencies for uplink messages intended for said access network, within a predetermined frequency band, called a “multiplexing band”. The complexity therefore rests mainly with the access network, which must be able to receive uplink messages transmitted at arbitrary transmission instants and over arbitrary transmission frequencies within the multiplexing band, while the terminals can be simple and inexpensive to manufacture.
Furthermore, the terminals preferably transmit without verifying the availability of the selected transmission frequency, in order to reduce the measures to be carried out and the associated power consumption.
To reduce the costs of implementing a wireless communication system for the IoT, it is also advantageous to use a freely available multiplexing band. For example, the ISM (“Industrial, Scientific and Medical”) band includes frequency bands that are said to be free in that they can be used without prior administrative authorization, subject to observing some regulatory constraints.
However, the result is that the level of interference within the multiplexing band can be great. As a result, if the terminal selects a transmission frequency without carrying out prior measurements, said transmission frequency can have a high level of interference, such that the transmitted uplink message will not be detected by the access network.
In order to overcome this problem, the terminal can, however, regularly select a new transmission frequency, in order to reduce the probability of all of the uplink messages from said terminal not being transmitted over transmission frequencies having high levels of interference.
If, generally, the wireless communication systems for the IoT can tolerate the possibility of some uplink messages being missed by the access network, there are nevertheless uses for which it can be necessary to provide a minimum level of quality of service.
For example, it can be necessary to ensure that at least one uplink message can be received by the access network over a predetermined duration period. In the case, for example, of remote reading of gas, water, electricity, etc., meters, the receipt of at least one uplink message over a period of one month can prove to be sufficient. In the case of remote monitoring of buildings or houses, and particularly in the case of a break-in or a water or gas leak, it can be necessary to ensure that at least one uplink message can be received over a much shorter period, for example less than one hour.